Water soluble films are commonly used for the temporary protection of various materials, articles and surfaces. A typical application is the enclosure or packaging of active agents, such as water soluble or water dispersible solid materials, for preservation until it is desired to add the agents to an aqueous medium. The active agents may be substances which are toxic or harmful if directly contacted by a handler or may be materials which merely are difficult to dispense in accurate amounts in bulk.
Typical of active agents packaged in this manner are household cleaning products such as soaps, detergents, dyes and bleaches; agricultural chemicals such as fertilizers, herbicides and fungicides, and pesticides such as insecticides and nematicides; industrial process chemicals such as carbo black, activated charcoal, biocides, and other functional compounds; pharmaceuticals including solids and liquids; and generally any agents requiring protection prior to being added to an aqueous medium.
Other applications include the covering or "shrink-wrapping" of articles with water soluble film for protection during display, storage or shipment, such as vehicles and recreational products used in water (boats, jet skis, and the like), food products, and other consumer products, materials and surfaces where it is convenient to remove a protective film by soaking in or spraying with water.
Representative of U.S. patents on water soluble films, film forming polymer compositions and packaging, and other applications of the films are the following:
U.S. Pat. No. 3,113,674, Kiefer et al., describes a water soluble, heat sealable, film forming polymer composition, for the packaging of detergents, bleaches, dyes and other products, comprising a mixture of a cellulose acetate sulfate and either a polyvinyl alcohol (PVA) or a polyethylene glycol.
U.S. Pat. No. 3,277,009, Freifeld et al., describes water soluble packages for detergents in which the water soluble packaging material is a polyvinylpyrrolidone (PVP) derivative.
U.S. Pat. No. 3,634,260, Pickin, describes packaging materials for bleach compositions based on PVA containing 12-40% of unhydrolyzed polyvinyl acetate.
U.S. Pat. No. 4,289,815, Lee, describes sealed pouches for release of chlorinating agents in which the pouch material is a cold water insoluble PVA film.
U.S. Pat. No. 4,522,738, Magid et al., describes a double envelope toilet bowl cleaner packet, each envelope said to be formed of a cold water soluble polymer such as PVA or a carboxymethyl cellulose. The envelopes separate an acidic cleansing agent and a basic neutralizer. Testing was at 70.degree. F.
U.S. Pat. No. 4,532,063, Gueldenzopf, describes a dissolvable bleach sheet is which the film forming polymer is a hydroxypropyl cellulose polymer.
U.S. Pat. No. 4,747,976, Yang et al., described packaging films for detergents in which the films are formed from copolymers of 90-100% hydrolyzed vinyl alcohol and a nonhydrolyzable comonomer such as an acrylate. The films are said to be stable over a wide range of temperature and humidity. Solubility was tested at 70.degree. F.
U.S. Pat. No. 4,801,636, Smith et al., describes polymer films prepared from blends of PVA, a crosslinking agent for the PVA (such as boric acid), and an alkyl cellulose or derivative.
U.S. Pat. No. 4,806,261, Ciallella et al., describes packaging films for detergents comprising laminates of PVA and a water soluble cellulose compound such as carboxymethyl cellulose (CMC), sodium salt, combined with cellulose fibers.
A major problem encountered in packaging or protecting with water soluble films is poor disintegration of the films when contacted with cold water (about 70.degree. C. or less). Poor disintegration is evidenced by failure to begin dissolving within a predetermined period (about 120 seconds or less), failure to dissolve at a sufficient rate, failure to dissolve cleanly (absence of lumps or stringy residue), or any combination thereof. In addition, improved cold water disintegration should be achievable without substantial loss of stability of the films over a wide range of storage and use conditions.
This problem is recognized in the following U.S. patents:
U.S. Pat. No. 3,695,989, Albert, achieves cold water solubility of PVA films at 40.degree. F. by incorporating gas bubbles in the films.
U.S. Pat. No. 3,892,905, Albert, describes polymer mixtures of PVA, PVP and a plasticizer as a means for improving cold water solubility of polymer films.
U.S. Pat. No. 4,481,326, Sonenstein, cites the foregoing Albert patents and describes a more specific combination of PVA and PVP as a means of not only improving cold water solubility but also resistance of the films to aging under various conditions of temperature and humidity.